Preheat the oven to 350°. Grease a small baking pan or casserole pan with butter or a little oil. Rinse off the fish fillets with cold water, pat dry. Use long nose pliers to remove any pin bones from the fillets. If you want, cut the fillets into large serving pieces. Place the fillets at the bottom of the pan, sprinkle with salt.
Melt the butter. Crush the Ritz crackers over a bowl; they should look like coarse breadcrumbs. Mix the melted butter with the breadcrumbs. Pack the crumb mixture over the top and sides of the fish fillets.
Place in the oven and bake for 20 minutes or until the fish flakes easily. (Thin fillets may take less time; very thick fillets may take longer.)